1. Field of the Invention
This invention relates to a novel process for control of Fusarium vascular wilt diseases and compositions for use in such a process. More particularly, this invention relates to such a process in which suppressiveness to such diseases is induced in Fusarium wilt conducive soil by adding to such soil a Fusarium wilt suppressive amount of a Fusarium wilt suppressive strain of the microorganism Pseudomonas putida, one or more Fusarium wilt suppressive ferric iron chelating agents, one or more of the ferric iron chelates of such agents or a combination thereof, and compositions for use in such process.
In a more limited aspect, this invention relates to a biologically pure culture of the heretofore unknown Fusarium wilt suppressive strain of Pseudomonas putida.
2. Prior Art
Vascular wilt diseases induced by the fungus Fusarium oxysporum are of considerable economic importance, annually causing millions of dollars worth of damage to important economic crops. Vascular wilt diseases occur on a wide variety of economic crops, including tomatoes, peas, bananas and cotton, often resulting in a considerable decrease in crop yields. Typically, depending on the environment and the severity of the disease, when plants become infected with these diseases, they become yellow, wilt and may eventually die if not promptly treated. The various forms of Fusarium oxysporum which are pathogenic to a large number of crops are widespread. Spores of the fungus are difficult to eradicate, and can survive in agricultural soils for many years.
Heretofore, several methods have been proposed for controlling vascular wilt diseases caused by Fusarium oxysporum. For example, various chemical methods have been suggested and several now enjoy widespread use. Although relatively effective, such chemical methods suffer from several inherent disadvantages. One such disadvantage relates to economies of obtaining an acceptable level of fungus control. Chemical control of Fusarium induced wilt diseases is expensive, and, therefore, can be used economically only in high income applications. Another such disadvantage relates to the level of control which can be obtained through use of chemical methods. Many of the various chemical fungicides that are recommended for use, such as benomyl, thiophantemethyl and thiobendozole are not sufficiently effective for widespread commerical use. Moreover, as disclosed in Erwin, D. C. 1977, Control of Vascular Pathogens, Pages 163-224 in: M. R. Siegal and H. D. Sister, eds. antifungal compounds, L. Manel Rekken Inc., New York, still another disadvantage is that these chemical fungicides have various physical and biological properties that greatly limit their effectiveness.
Eradication of Fusarium wilt pathogens by application of steam and various soil fumigants has also been recommended. Relatively effective short-term control is achieved by these procedures, especially if steaming is combined with the use of a fumigant such as metam sodium. However, one disadvantage of the procedure is the lack of long-term control because the pathogens survival structures (chlamydospores) are at such depth in the soil that complete eradication is almost impossible.
Several investigators have evaluated soils which are naturally suppressive to certain plant diseases, including Fusarium wilt diseases. In one such evaluation, various un-identified fluorescent psuedomonads were implicated as the suppressive factor in wheat take-all decline soil. In another such evaluation in Sher, F. M. and R. Baker, "Mechanism Biological Control in Fusarium - Suppressive Soil", Phytopathology, 70: pp. 412-417 (1980) experiments were described in which addition of a certain fluorescent pseudomand identified only as Pseudomonas sp., which had been isolated from Fusarium wilt suppressive soil, rendered Fusarium oxysporum conducive Fort Collins clay loam suppressive to Fusarium wilt of flax. Similarly, various non-Psuedomonad strains isolated from take-all decline soil have been reported in Kloepper, J. W., J. Leong, M. Teintze, M. Schroth, "Enhanced Plant Growth by Siderophores Produced by Plant Growth Promoting Phizobacteria", Nature 286; pp 885-886 (1980), as controlling take-all of wheat, and other non-Psuedomonad microbe strains have been shown to control Fusarium wilt in flax.